"A person has been arrested on suspicion of sending a suspicious letter," the FBI said in a statement.

The detainee suspected of being behind the toxic consignment to Trump is a female Canadian citizen, an anonymous source with insight into the ongoing investigation told the news agency Reuters.

The package was discovered last week during a routine check of the post office at the White House and thus did not reach the president.

Since then, the US police and intelligence services have investigated who is behind the shipment.

The border between the United States and Canada

The suspect was arrested at the US-Canada border in Buffalo, New York, a Border Police chief told AFP.

According to American media, the suspect must have had a gun on him at the time of the arrest.

Previously, two people in two separate cases have been sentenced to prison for sending ricin-contaminated letters to Barack Obama during his time as president of the United States.

One of the most toxic substances in the world

Ricin is found in the seeds of the plant of the same name and is one of the world's most toxic substances.

The toxic protein ricin can cause vomiting, internal bleeding, difficulty breathing and lead to death.